The present invention relates to a method and an apparatus for improvement of transmission quality in a point-to-multipoint radio transmission system, comprising at least one base station and a plurality of participant stations, in which the radio transmission region belonging to each base station comprises one or more sectors and the base station has a transmitting and receiving unit for each individual sector so that data transmission can occur between the transmitting and receiving unit for each sector and the participating stations present in that sector. This type of point-to-multipoint radio transmission system is, e.g., described in German Patent Application DE 44 26 183 C1.
Radio transmission systems, which may be terrestrial radio relay systems or satellite transmission systems, allow new radio links to be installed very quickly or existing ones to be completed. The available frequency spectrum should be used in as optimum a manner as possible with such radio transmission systems. In a point-to-multipoint radio system according to German Patent Application DE 44 26 183 C1 the transmission capacity is adjusted or fit in a flexible manner to the requirements of the participant so that the bandwidth of the individual transmission channels is adjusted to the data transmission rate required by the individual participant stations. Here a variable adjustment of the modulation method (e.g. N-PSK, with N=4 . . . 16 or M-QAM with M=4 . . . 256) is also provided in the individual transmission channels.
In order to guarantee high transmission quality in a radio transmission system, disturbing interferences should be avoided as much as possible. Moreover geographic conditions which can cause interference are already considered in radio field planning. Interference can arise in a base station or a participant station by reflection of the transmitted signals themselves until the loss level can extinguish the signal. Also signals from neighboring radio transmission regions can cause interference at a participant station or a base station. Generally interference cannot be sufficiently accurately determined in advance by radio field calculations during the planning phase of a radio transmission system. This is particularly true because of changes of terrain structures, vegetation or house building, or completion or change of the radio network during operation of the radio transmission system.